Well... I'm very glad that the first three episodes exist, and that the ending wasn't a copout about "the real past was the friends we made along the way" or "Jack uses his one chance to go back and save Ashi."
Other than that, I think that Ashi's characterization was all over the place, the final episode felt super cookie-cutter, the tone shifts were extremely weird, and the subplots (Jack's lost sword + Scaramouche racing to tell Aku about it in particular) felt extremely oddly paced to the point of completely undermining themselves. Also. while I get that behind shackled to the Guardian premonition of Bearded King Jack over a decade after you wrote that scene and got new ideas must be a sticky situation, but having the solution be handwaving it away as "oh, the magical time portal was wrong about seeing the future, and the Guardian died" almost made it feel like they shouldn't have even bothered bringing it back up if that was their answer.
And yeah, the ending "twist" being Gurren Lagann but... far less competently executed (love interest is daughter/creation of the bad guy, is transformed into inhuman thing to fight against hero after they find love together, fights back with the power of love, fades away during wedding) is... I almost found it funny, which I don't think they intended.
